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Can some one please explain to me the purpose of the combustion chamber?
Please, i need some one to explain to me the purpose of the combustion chamber in a jet engine, why do we need to burn the gases to get energy ? the compression does not suffice ??
is it possible to explain from an "Energetic" point of view ?
thank you

Can you explain your thought process on this. What is going to compress the gases? Are you trying to invent a perpetual motion jet engine? (You won't get a patent for it.)

No i just want to know exactly what is the purpose of adding the combustion chamber if gases are compressed with the compressors ?
(is the compression ratio not enogh to spin the turbines ?)

How are the gasses compressed? (I'm trying to get you to think this through.)

(As i know) by the rotation of the compressors (LP and HP)

Correct. So what turns the compressors?

Review https://en.wikipedia.org/wiki/Conservation_of_energy

You need some energy to compress something. Where are you going to get the energy from?

See this physics.SE question

thank you all for the help
can some one explain this
"" Now the combustion heats the gas up, and makes it expand ""
what exactly happens when the gas expand ?

@Transistor that may not be the correct way to bring the user to the answer because you don't have a compressor in ramjet engine still it has a combustion chamber.

OK, this answer will definitely be trumped by better ones, and Google will serve you better, but until then....
Thrust is basically throwing a mass of stuff in the opposite direction you want to move in. The more weight &/or speed you can throw it, then more thrust.
We want to throw air (because there's a lot of it around, and it's what we want to be thrusted about in).
You could produce a small amount of thrust if you just squirt highly compressed air or steam through a nozzle, perhaps from a storage cylinder; the greater the stored pressure or amount, the faster or more of the air escapes, the greater the thrust. You would need a vast amount of stored air to do this for any length of time.
So, a glorified deflating party balloon.
You could produce a small amount of thrust if you squirted a fuel, with enough air to burn, into a chamber with an opening at one end; the more burning fuel, the greater the expansion & the faster the hot gases escape through the opening, the greater the thrust.
But it would really just be a noisy barbecue.
You could combine these two things, using the compressed air to considerably increase the amount of fuel burnt in the chamber, increasing the thrust.
Then you'd have a very hot, very inefficient rocket engine.
However, if at a point just after the fuel has completely burnt in your chamber, you stick a fireproof windmill (turbine)  into the flow of escaping gases, driven by this flow to turn a shaft and connect that shaft of the windmill back to a point where the air is coming from before it is mixed with the fuel, to a fan (compressor) that is turned by the shaft to drive the flow, then the faster the turbine is turned, the more air can be supplied by the compressor, to burn even more fuel, which in turn means the turbine is turned even faster, which turns the compressor faster so yet more air can be supplied, and so on.
So the burning fuel becomes expanding gases which accelerate the turbine, which powers the compressor, which allows more fuel to be burnt under higher pressure, to accelerate the turbine. The air can just come from the atmosphere in front of the inlet to the compressor, rather than having to be stored in a compressed form.
You could divert some of the air from the compressor (it's now compressed & can be plumbed like a fluid, going through tight turns & small holes)  to form a cooling shield around the flame so you don't melt the walls of the chamber.
In fact, once this process get going properly (it is not self-supporting until quite a high rpm), the compressor can supply much more air than is needed by the fuel, and this can be used  to cool parts of the engine & can be added to the exhaust as extra thrust.
So, starting at the air inlet, there's a compressor stage, then a combustion area, then a turbine stage, then the exhaust.
And you'd have a gas turbine engine. The combustion chamber is obviously vital to this process.
Gas turbines actually use a huge proportion of their energy just to keep this process supporting itself; what energy there is left over - just shooting out the back (turbojet) or driving additional turbines to turn fans (turbofan) or propellers (turboprop) or helicopter rotors or ships propellers or generators (turboshaft) - can still be considerable. The faster it goes, the more power.
Gas turbines have amazing power to weight ratio. You & three friends could manhandle a PT6A into the back of a station wagon; it produces the same power as a small rail locomotive. Unfortunately, gas turbines are not suited to constantly changing their power output like a car engine, and don't use that much less fuel when idling than when flat out.
It's an application of the Brayton Cycle; it's thermodynamics. It gives you a truly enormous increase in power because you can utilise the ability of stored fuel to create heat & expanding gas by burning it in really carefully controlled extreme conditions. In the combustion chamber.

An interesting, vivid, and relatable explanation at a very basic level. I upvoted it. And I like the first sentence as a way of expressing that more formal answers will be in order and that the information is readily available elsewhere.


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How are engines numbered?
On a commercial aircraft, the number of engine is usually 2, 4 or 6. When the technician or LAE was given task to inspect an aircraft engine no 2 on a 4 engine aircraft. Which engine would they go to?
2 different lecturers of mine had 2 different answer for this and both have experience in working with aircraft engine.
Lecturer A said:

Lecturer B said:

Which one is right? Requesting help from Technician or LAE. A brief explanation would be really helpful too.

"Lecturer form commercial industry experience" may be quoting start-up sequence rather than identification sequence (tho' it's still wrong for the 747.) Lancaster start sequence is 3,4,1,2, so start sequence is NOT identification sequence.

According to my knowledge, aircraft engine would first start on even number on even date and odd number on odd date to reduce wear on just one engine upon starting. For Lancester part that would as well be a new info for me.

@cat Engine start sequence is usually determined by systems. On most aircraft this is the engine that has the hydraulic system that powers primary brakes or parking brakes. I don't know any transport aircraft where it is advised to switch by day.

Aircraft engines are ALWAYS numbered from left to right when viewed from the pilot's seat. Additionally, the start sequence is ALMOST ALWAYS number three, four, two, one. There are several reasons for this sequence: Number three engine starter distance from the battery(s) is the shortest The longer the distance the less amps delivered. Jet aircraft like the B-707, DC-8 had the pneumatic air connection close to the Number 3 engine. Once the number three engine was started it helped pressurize the pressure manifold for assisting the additional engine starts. Remember, a low start pressure could result in a hot start. Secondly, hydraulic pumps were located on the inboards #2 & #3 engines on the DC-4, DC-6, DC-7 & DC-8 as well as the B-707 (the B-747 had hydraulic pumps on all four engines plus an APU but the start sequence remains the same). It's never a good idea to have an engine running without full hydraulic pressure available to the brakes. Thirdly, passengers or cargo is loaded from the left side of the aircraft. By starting #3 & #4 first, last minute changes could more easily be facilitated with #1 & #2 dead. Boarding an aircraft behind an idling engine is always an interesting experience. Starting the #2 next would give additional hydraulic back-up and then allow the fire guard to move to the #1 engine and exit to the left. Lastly, by delaying the start of #1 & #2 engine, interior noise would be kept at a minimum for passengers and crew until all the cabin doors were closed.

747 Thrust Levers, numbered by respective engine numbers.

Please cite your image sources.

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Is feather edge bad?

Currently learning about aircraft piston engine. Feather edge can be found at the engine valves as according to the picture. Can someone explain briefly about what is feather edge? Why it is bad? Which part of the engine that has the feather edge?

http://content.aviation-safety-bureau.com/allmembers/faa-h-8083-32-amt-powerplant/sections/chapter-10.php There's a reference to feather edge in there, describing an improperly maintained piston engine valve.

Hello there, I'm sorry for the confusion and lack of explanation, the term "feather edge" is actually found on the engine valve. Thanks to all for trying to help me here. As aerobot has link a website to the AMT I had found the solution.

As noted here

A thin edge is called a feather edge and can lead to preignition; the
  valve edge would burn away in a short period of time, and the cylinder
  would have to be overhauled again.

Basically during a rebuild over-grinding the valves can lead to a feathered edge which in turn can lead to higher/faster engine wear. Essentially by grinding the edge to thin you cause the limited remaining metal to wear out much faster. This can also lead to valve seating issues and out right leaks.

this is the answer i'm looking for. thanks

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Why was the Me 262's top speed at 6km?
The P-80 had its top speed at sea level, but the Me 262 achieved its top speed at 6km altitude. What were the reasons for this? Was it that the engine was designed for such an altitude to deal with high altitude B-17 raids? And if so, how specifically did they tune the engine for altitude?
from USAAF Wartime Tactical Planning Characteristics & Performance Charts (Page 44 of the PDF)

from post-war British test flights of Me 262 (Page 5 of the PDF)

Where do you see referenced the P-80's top speed occurring at sea level and the Me-262's at 6km?  Neither of those sounds intuitively correct, but I'd be interested to see what source they're from.

@Ralph J I updated the post to include sources

Are the quoted speeds CAS, EAS, or TAS? Are the two data sets using the same airspeed? It could be the difference.

@Gerry They're both definitely TAS. No doubt about it.

It has to do with the engine design, as follows.
The higher a plane flies, the faster it can go for the same engine power. This is because as the air thins out, drag decreases. However, as the air thins out, the amount of oxygen available to burn the fuel decreases and so the engine puts out less power the higher it flies.
There comes a crossover point where the drag decrease with increasing altitude is cancelled by the power decrease with increasing altitude, This is called the critical altitude. If you trim the plane to fly higher than this, you go slower and at some point you get boxed in by the stall speed and you cannot fly higher.
For a turbojet, you add altitude capacity by adding compressor stages to jam more air into the engine, which pushes the critical altitude up. So the performance difference between those two planes boils down to how much the compressor stage of each engine boosts the pressure in the combustors.

Thank you. If you may, there is one question I still have. Even though you can increase altitude performance by increasing total pressure ratio, the general shape of the alt vs thrust curve would stay the same, wouldn't it? Being max at sea level and gradually decreasing up to altitude? Adding compressor stages would only shift the curve to the right, wouldn't it?

I am no expert, but this is how I understand it:
All air breathing engines lose power as you increase altitude due to decreased air density. This also means leases drag at high altitudes, but the loss of power was greater than the loss of drag.
Early jet fighters like the P-80 and F-86 had their max speed at sea level because of this.
Engine design eventually changed so that the rated power was limited or restricted at lower altitudes. This is called a “Flat Rated” engine. Aircraft with flat rated engines could maintain this artificial rated max power to higher altitudes which meant their max speed was no longer at sea level.
The Me 262 may have had “flat rated” engines, but I suspect there may have been some other limitations that resulted in slightly less speed at lower altitudes.

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What are these windows/portholes on the English Electric Canberra bomber?
This may be an obvious question, but I don't know, which is why I'm asking here. I've searched "Canberra canopy porthole" and "window", but didn't get any information. There is a porthole of sorts on the left side of the canopy of this bomber, I'm wondering what it's for.

Photo source.
Here is a view from inside the cockpit:

Photo source.
There also appears to be a similar thing on the bottom of the nose of the aircraft, offset to its right. The following is a screenshot from a video game, as I wasn't to find a photo of this.

I'm tempted to say that this second one is to do with bomb sighting, however if it weren't there, the bomber would have just as good a view, wouldn't they?

A blown, spherically shaped plexiglass dome will never have the optical qualities of a flat piece of glass, especially with the production technology of the late Forties. So yes, the nose cone window is for bomb aiming.

You beat me to it w/ your comment Peter-- was in process of adding to my answer

It's called a "Direct Vision" (DV) window. The canopies are sealed shut, so the small DV window is provided as a way to open a small hole if required. For example, to communicate on the ground or in the event of icing or other canopy issues.
Edit: I wasn't able to find a formal source, but this page is fairly authoritative:
http://alverstokeaviation.blogspot.com/2016/08/english-electric-canberra-technical-tour.html

Note the wires going to it-- it is heated, don't you think?  If it opens, can you identify where the handle or latch is?  So perhaps it is heated AND it can be opened?

Is this both the case for the canopy one and the one on the lower nose? Would you open the port/window completely? If so I'd imagine enormous amounts of wind entering the cabin. @quietflyer Yes, I did notice the wires. Not sure what they're for.

@quietflyer It certainly makes sense to be heated. It looks pretty clear that the bottom is hinged (7 O Clock our image), with a secured (thumbscrew) handle at the top (1 O Clock)

I'm thinking that part of the reason it exists, is so it can be heated more strongly than the plexiglass could be.  In other words it is glass and can take the direct heat of a heating element that would melt the plexiglass.  This answer could be improved by incorporating that idea.

That's a very interesting link. In that model the bottom flat window seems to be for bomb sighting. It is also centred, as opposed to the offset ones to the side in my images.

Re the upper "porthole"-- it sure looks like a heated panel for clear vision in extreme icing.  Note the resemblance to a "hot plate" in King Air etc.  It is undoubtedly glass and can be heated by a heating element (note the wires) to much higher temperatures than the perspex canopy could tolerate.  Note that there is one on each side, and this aircraft has side-by-side seating in the cockpit.  As has been noted in another answer, it appears to have a hinge and a thumbscrew latch, so it could be opened if needed (e.g., a/c is heavily iced up and electrical power has been lost or can't keep up with the icing-- or just to talk to someone on the ground.)
Your question also references the flat panel on the transparency on the lower part of the nose.  It is not clear from the photos whether this is heated or not; it's almost certain that this larger flat panel could NOT be opened.  However you'll note that it is very common for aircraft to include a flat glass panel for aiming a bombsight or as a window for a camera in the case of a reconnaissance aircraft.  The curved perspex of the rest of the transparency will always have some optical distortion.  Note that until fairly recently, many fighter aircraft had a flat windscreen in front of the pilot.  Again part of the reason for this was to prevent optical distortion as the pilot looked through the gunsight.  If this weren't an issue, the thick armored flat glass of the windscreen could have been "faired" more smoothly by an additional curved piece of perspex in front of it, but this was only rarely done.

I'm not a Downvoter, however, "Probably a (guess)" is a very poor answer.

Well, I don't think so.  Anyone who's seen a "hot plate" in a King Air etc would note the strong resemblance but it's only appropriate to note that one doesn't actually know this for a fact.

If we are waiting for a design engineer or pilot to provide a definitive answer we might be waiting a long time.  A credible, well reasoned educated guess goes a long way towards generating useful discussion and enhancing understanding.

Was starting to type the additional info as saw your comment Peter

This is a good answer now. It also answered another question that was in my mind, why do fighter aircraft have a flat glass front portion on the canopy given that it sacrifices aerodynamics. I think maybe because it's usually thick bulletproof glass, but the view distortion reason seems true also.

@quietflyer I did not downvote, but a person can only downvote once, regardless of how many times the answer has been edited. As of me writing this, this answer has +3/-2.

Clicking the "up" or "down" button on a post you've already voted on will remove your vote, not add a new one. You can only remove your vote or change an upvote to a downvote (or vice-versa) within a certain period of time or when the question is edited, you cannot vote multiple times.

Ok so you are saying that the vote can be CHANGED after an edit but an additional upvote/ downvote cannot be ADDED after an edit.  Thank you for the clarification.  That is a good system and I'm glad it's that way.  I am going to delete my comments re that issue.

This is begging for an answer to why other jet aircraft don't have it (it could be included in this answer).

Good point-- I've got to go do something else now but....

I was a Canberra pilot back in the day.  The porthole in the canopy was simply a way for the pilot to see his way if the canopy misted or iced up, simple as that.  In fact I never had to use it.

Welcome to Av.SE!

The panel in the nose cone was a piece of optically flat glass to avoid distortion which would affect the bomb site, and/or to give a camera a clear view forward.

the DV window was used by aircrew , open the dv and stick your hand out, to indicate to the ground crew that the aircraft in now depressureised and that it was safe to open the side door (strike wing RAF Akrotiri)


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What API can I use to get FAA NOTAMS or will this one I found work?
I am not sure if this is the correct place to ask this because it has to do with APIs with XML/JSON/SOAP, but it also has to do with aviation.
I am in dire need to find an API associated with the FAA to get NOTAMs for areas and airports. NOTAMs are Notices to Airmen, and it will be a useful feature in a service I am creating.
I have done extensive searching for a NOTAMs API, but I cannot find anything except this:
https://notams.aim.faa.gov/notamWFS/
However, this website requires registration which is just a broken link. Any suggestions on how to use this?
Do you know of any other NOTAM APIs available?
Also, if possible, do you know of a weather API which has the same information included in an ATIS/AWOS reporting station?
I was able to find working APIs for US regulations and general weather (not specific enough) and pilot information, but I cannot find any for specific weather or NOTAMs.
EDIT: A friend of mine was able to click the registration button, and it didn't give him an error. He sent me the link and I am now trying to register on the site I found.

If this path does not work, you could still build your own API by scraping the adequate pages. Might end up being somewhat more flexible than  dealing with XML/SOAP requests.

That approach has a downside @Stanislasdrg, website changes can leave developers scrambling.

@Forseth11, the ICAO has global notams database which may be of interest: https://www.icao.int/safety/iStars/Pages/notams.aspx.

@GdD it works! Thanks so much!

How long did it take them to approve your request? Have you tried www.aviationweather.gov for weather?

Echoing Aviaton Weather for METAR information. Provides JSON formatted data based on given inputs (GPS, station code).

As @GdD mentioned in the comments, there is an API for NOTAMs here: https://www.icao.int/safety/iStars/Pages/notams.aspx
You also asked for metars, which you can get from here:
http://tgftp.nws.noaa.gov/data/observations/metar/cycles/${TIME}Z.TXT where ${TIME} is the hour of the Zulu time you are interest in, wrapped between 0 and 23 (eg. 16)


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What to look for when purchasing a headset
I'm currently a student pilot, and I'm starting at an aviation university this fall to major in commercial aviation. Needless to say, I will be flying a lot. I'm looking to upgrade to a nice headset from the pretty basic one I have now, and I'm looking for a bit of guidance. I'm 6'3, so I wouldn't say I have a small head, and I've had problems in the past with headphones feeling cramped on my ears, which I don't want to be the case with my headset. I plan on having this headset for a while, at least all the way through college and hopefully several years after that.
First of all, is noice-cancelling actually that important(in terms of health and comfort)? I know there are a few decent headsets are out there w/o noice cancelling, and they are quite a bit cheaper than noice cancelling headsets.
I've been told about a couple commonly used expensive headsets that are pretty widely used across the industry. However, these headsets are $850+. At this price level, does the price of the headset accurately reflect quality, or is everything more personal preference? What are some of the pros and cons of the more popular headsets, and what should I look for when purchasing one?

Shopping questions are unfortunately off-topic here. If you can edit your question to remove the "product specific" or "product recommendation" parts, I think it could be a good question.

David Clark are good too.  I upgraded my non-noise cancelling DCs to noise cancelling with a kit from Marv Golden many years ago.  Taking out all the low frequency vibration/noise really makes hearing ATC a lot easier.

I recently bought 2 pair of noise cancelling headsets from Headsets Inc, Model DRE-6001 (several colors available) with the music-in jack (which I checked out, but don't actually use in flight, lot of ATC to listen to in my area).  The noise cancelling works very well.   I highly recommend noise cancelling to save your hearing, and to make flights more comfortable mentally. $400 plus shipping.

“But it nice or buy it twice.” Cheap products usually cost more over time than quality ones. A good headset can easily last decades if you take care of it, while cheap ones may need to be replaced every few years.

I've had problems in the past with headphones feeling cramped on my
  ears, which I don't want to be the case with my headset

Do your best to test them out before you buy. Some pilot shops will let you put them on your head and if you are nice to the people that lurk around the airport they may lend you one for a flight to try out. I find that the Zulu's have bigger ear cups than the Bose but I don't have any hard numbers on size this is personal experience wearing them.

First of all, is noice-cancelling actually that important(in terms of
  health and comfort)

Yes, just ask any one that flew in the pre-headset days. I personally find that I can comfortably fly for longer times with an ANR headset. Another thing to note is that the ANR head sets tend to not squeeze your head quite like the passive headsets I find this to be the real gain in comfort.
One of the big functional differences is that some of the LightSpeed headsets do not cary a TSO, I belive all of the Bose do. This may impact your ability to use them for commercial purposes in the future. You can find a discussion on it here.

Good headsets are expensive, but an investment as they aren’t something you purchase every few months, you keep them for years - which makes the decision all that much more tricky.
Factors to consider:

ANR vs PNR

With regards to active noise reduction in a headset, it makes a huge difference. It is significantly quieter, giving you clarity in busy airspace calls and obviously, and most importantly they mitigate damage to your hearing - cockpits are loud, especially helicopters. Be weary though, their battery’s last only about 40 hours and although they will still work when this happens you won’t have ANR and it is much worse than passive headsets at this point, almost unbearable to fly with. PNR don’t need batteries, only advantage.

Impedance, high or low.

Without getting too technical, civilian aircraft use high impedance electet microphones and military/ex military aircraft use low impedance microphone. You most likely will fly Pipers/Cessnas/Robinsons, so get high impedance.

Plugs
a. Dual Male Plugs - Fixed Wing
b. Single Male Plug - Helicopter
c. Panel Powered plugs - Here are various types but the most applicable to your case would be lemo - most newer aircraft have these plugs and allow you to use your ANR headset without batteries.

Bluetooth

It’s maybe an extra $100, but it’s already so expensive don’t regret not having spent extra cash early on. What will you connect it to? Music, maybe. Modernised instrument panels or iPads with aural flight information, yes, and it lets you make a phone call, although it’s not permitted in flight - it doesn’t stop many pilots, it may just come in handy.

Brand

The competition gaps have closed but the biggest international brands with good after purchase service are David Clark, Bose and Lightspeed. New contenders may have joined the game and are owed a consideration as well.
Consider a high impedance Bose A20 lemo with the appropriate fixed with and/or helicopter adapters and Bluetooth. Most adaptable option with excellent after market service. This is what I have experience with.
The Lightspeeds are really nice but I have no experience.
The David Clarks are my favourite PNR headsets.

While "comfort" may seem like a luxury, it's no fun to fly around with a headache.  Give them a good try and look for minimal "squeezing" pressure.  Also see other answers and comments re taking hearing protection seriously.  Also if you routinely wear glasses (including sunglasses) be sure to test while wearing them-- they may break the earcup seal in a way that lets more noise in, or they may cause uncomfortable pressure points.

When I got my pilot's license in 1978 my instructor said...

"If you are going to fly for a living and want to look professional while you
  gas up,
  you should pay the exorbitant price for a pair of Ray Ban sunglasses, a
  David Clark headset, and Jeppesen charts.
If you want to save \$1500, you can buy a pair of \$2 polarized
  sun glasses, a \$100 FlightCom headset, and use free Govt charts. They will work just as good!"

The one thing that made more difference in my comfort than anything else was using cloth ear protectors. They are more comfortable than any ear cushions I have tried, and allow a constant supply of cool fresh air to breath past your ears.

Cloth ear covers allow fresh air to breath past your ears and prevent sweating.
I have tested ANR and they make a huge difference in eliminating background noise. While they are worth the extra money if you have it, I have other things more important to me for $500 and have never purchased a pair.

What's your hearing worth to you? Noise exposure over time will cause hearing loss. Every little bit of protection helps reduce it. If you think ANR headsets are expensive, check out the price of hearing aids.


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Is it legal for one nation to issue notams for territories in another nation?
Is it legal (as in "is there international agreements not do so") for country A to issue NOTAMs about some territories in country B. Does it matter both A and B recognize each other?.How such things are handled? Does such NOTAMs were issued in reality?
Like:

FAA declares NOTAM about Heatrow airport in UK
Argentina's equivalent of FAA issues NOTAMs about Falkland Islands.
PRC issues NOTAMs about Taiwan.

Never heard of international agreements on that subject, but I would say, yes.  If an NOTAM about another nation is pertinent to pilots traveling there, or means to alert pilots of hazards associated with nations unfriendly to your state, a NOTAM makes sense..

This might be a better fit on Law SE. But really, why might it not be legal? It is a notice, just a possibly useful piece of information. There’s no jurisdiction implied, and they are really just relaying information that’s already out there.

@MichaelHall notams have legally binding status. If the FAA issues a NOTAM declaring a no-fly zone, anyone violating that will be in serious trouble. Now consider China declaring a no-fly zone over all of Japan, South Korea, and Taiwan and setting out to enforce it with their armed forces. If the NOTAM were legal, them flying their jets over Japan and shooting down Japanese and other airliners on the way to Tokyo would in your world be perfectly fine as they were just enforcing the NOTAM they created.

I think Cyprus is a perfect example. The border dispute there also shows in an ongoing NOTAM battle, each issuing NOTAMs over what they consider their own airspace.

@jwenting, I’ve enforced no fly zones, they aren’t  created or promulgated by NOTAM!  No fly zones are created by UN Security Council resolution, or state department/ congress.  Armed enforcement over sovereign territory is WAY out of the scope and intent of FAA jurisdiction and the NOTAM system.  You’re comparing “fyi, taxiway B is out of service for construction…” with overt acts of war.

@MichaelHall This issue came up after the shootdown of MH17 over Ukraine. The FAA NOTAM A0004/22 bans flights in Ukraine and says "THIS NOTAM APPLIES TO: ALL U.S. AIR CARRIERS AND COMMERCIAL OPERATORS; ALL PERSONS EXERCISING THE PRIVILEGES OF AN AIRMAN CERTIFICATE ISSUED BY THE FAA, EXCEPT SUCH PERSONS OPERATING U.S.-REGISTERED AIRCRAFT FOR A FOREIGN AIR CARRIER; AND ALL OPERATORS OF CIVIL AIRCRAFT REGISTERED IN THE UNITED STATES, EXCEPT
WHEN THE OPERATOR OF SUCH AIRCRAFT IS A FOREIGN AIR CARRIER." These are who the FAA has authority over.

@user71659, That would have been an excellent example to include in the question, and I might later address it in my answer.  However, it neither negates the basic truth of my answer in 99%+ of NOTAMS, nor does it bolster jwenting's comparison.  Yes, the FAA does have jurisdiction over US Carriers and crews operating overseas, and it makes sense to prohibit them from flying into active combat zones.  But they cannot issue a blanket no fly zone of the sort that has persisted over Northern and Southern Iraq which most people are familiar with.

@MichaelHall the FAA constantly created temporary no fly zones through NOTAMs for things like presidential visits, major sporting events, and things like that.

@user71659 mind that that's a restriction applying only to aircraft under FAA regulations, so US registered aircraft. The FAA can't tell say Japanese aircraft that they aren't allowed to fly over Japan (or over Ukraine), only that they can't fly over the US.

@jwenting, those are called TFRs, (temporary flight restrictions) they are not no fly zones. You may fly through them under certain conditions. Pilots are informed of TFRs through the NOTAM system, but don’t confuse the two - an OTS is as much a NOTAM as a TFR. And the question wasn’t about TFRs, or FAA restriction on US carriers and crews flying over combat zones. It was a generic question about generic NOTAMS which overwhelmingly consist of mundane airport information. If you want to presume otherwise you are welcome to provide an answer based on your interpretation of the OP's intent.

Yes, it is perfectly legal for one nation to “publish” a NOTAM for territories in another nation.
(I changed your wording from “issue” on purpose, I will explain at the end once I have established the basis for it…)
First, let’s define what a NOTAM IS:
From the FAA:

A NOTAM is a notice containing information essential to personnel concerned with flight operations but not known far enough in advance to be publicized by other means. It states the abnormal status of a component of the National Airspace System (NAS) – not the normal status.

More information can be found on the FAA website here:  FAA NOTAMS
Another good definition from Theconversation.com:

The NOTAM system is a computer network run by the Federal Aviation Administration that provides real-time updates to crews about situations relating to weather, infrastructure, ground conditions or anything else that may affect the safety of flight.

To summarize, the NOTAM system is means for dissemination of information in a positive and collaborative manner for the purpose of enhancing awareness and safety for flight crews and passengers.  It is managed between friendly nations in a cooperative way.
Next, let’s define what a NOTAM is NOT:
An instrument of foreign policy or means to impose political will over a sovereign nation.  Nor is it a means for the FAA to impose regulations domestically, that's what the FARs are for.
Finally, let's discuss how it works: (disclaimer – I have never participated in the creation or distribution of NOTAMS, but have been a user of the output for years and have an educated feel for how things work)

Local airport authorities and ATC have information that is useful.
They enter the information into a database of some sort.
The NOTAM system provides the means of distribution.
Users extract this information as needed.

To expand on your Heathrow UK example, let's say a maintenance worker driving around the airfield notices a pothole that needs fixing on taxiway B.  He/she would notify their supervisor who would notify the airport manager. The airport manager would then coordinate with ATC as well as maintenance to decide on the best time to close that taxiway to fix the pothole.  Once a decision is made, that information would be uploaded into a database so that the FAA can disseminate it through the NOTAM system.  Any crews going to Heathrow during that time would then know what to expect.
For another example touching on "no-fly zones" mentioned in a comment, let's say local ATC decided to issue a TFR (temporary flight restriction) because King Charles scheduled a PR Tea visit to the controllers in the tower. Same thing, this local TFR would be uploaded into a database for the FAA to extract and publish as a NOTAM.
In other words, the information published in NOTAMS is "grassroots", meaning it originates locally and is pushed up to a central location.  The FAA knows nothing of detailed ground operations at Heathrow or the King's tea schedule, so they would not, and could not actually create anything. It isn't their jurisdiction, they have no authority.
Getting back to your word "issue"; if you meant simply that they distribute the information then you could say they issue a NOTAM.  But they aren't the originators, they simply publish them using the NOTAM system as a conduit, and this is totally legal.  It is likely even required in some cases per IACO agreements.
Questions about how nations deal with border disputes is outside the scope of aviation, and is probably a better fit on Politics or Law SE.


text:
Should I add balloons in my Ultralight wing to help it float if I land in the water?
I like to fly over rivers and lakes in my ultralight. One of the things that scares me the most is if my engine died, I might drown down in the depths of the water as I egressed out of my ultralight.
My Hy-Tek Hurricane has an aluminum front and rear spar, with a few spreader tubes, and then it has simple aluminum tube ribs which slide into pockets in the Dacron wing covering. This leaves nothing but empty hollow space inside 99% of my wing.

Has anyone ever thought of adding some lightweight durable air-filled balloons inside their ultralight wing to add buoyancy in case of a water landing which would almost certainly flip my tricycle gear ultralight? As it is, the wing has plenty of gaps in it which would allow water to rush inside and sink my plane. I don't know how long that would take, but I would rather not find out!
My aircraft weighs just slightly less than 254lbs. So I would need approximately 254/8 = 31.75 gallons of air to maintain a neutral buoyancy, and I would probably want to add another 30% or so to that to turn my ultralight wing into basically a flotation raft if I ended up in the water.
So does anyone have any good ideas on what to stuff inside my wing so my little "ultralight" doesn't turn into an "UltraAnvil" and sink to the bottom with me drowning next to it? If I crashed in the water, I figure I probably have a 50/50 chance of extricating myself from the wreckage without drowning right away, considering the impact will probably knock the wind out of me. It would be difficult, but I think I could do it. If I was at a full stall when I touched down I think I would survive, but would certainly flip upside down, then it would be a mad scramble while upside down underwater to get the safety belt off and yank my helmet and it's wires off and kick free.
But if I CAN get out, the next problem is that I am fully clothed with shoes, maybe a ski jacket, gloves, jeans, thermals, and everything else. I have had an unlucky experience of being fully dressed while flailing in the river before when I dashed out to rescue an R/C plane once, and it was very dangerous, and I nearly did drown (I will never do that again!).
It sure would have been nice to have a partially sunk ultralight next to me to hang onto! So I was thinking balloons, because that would be easiest. I could just inflate maybe 100 balloons or so and then stuff each of them up in the zippered inspection seams, 50 in each wing. The weight would only be maybe 8 ounces or so of all the balloons, and I can't imagine that they would hurt anything inside the wing. Is this a good idea?

Do you sit above the wing or below it?

Below the wing. The aircraft configuration is a typical "Cessna-type" 4-axis control with horizontal and vertical stabilizers.

https://www.google.com/search?q=floating+ultralight&client=firefox-b-ab&tbm=isch&source=iu&ictx=1&fir=6w9vGbnDWJtkTM%253A%252C1SoBZ3RxghMjLM%252C_&usg=_2Nweqs2CFKgc6DPmGpTsrKingAc%3D&sa=X&ved=0ahUKEwipyIr21NPbAhWDQpAKHYyVCE8Q9QEIVTAN&biw=1600&bih=786#imgrc=

Any idea how much volume you're talking about inside the wings?

Go to a local pool and practice swimming in full gear. Keep in mind you can undress while in the water (you'll have to strip off the wet clothes anyway once on shore to avoid hypothermia). You could also use the stripped clothes as a makeshift flotation device by tying up the sleeves.

If you are flying over water, while not regulation, it would behoove you to have one of these on at all times. $140 is a small price to pay for floating, and you'd probably pay that trying to pack balloons in your wings or seal them up. You should also have a "quick release" seatbelt that comes completely off in one movement and works under tension (if you are upside down and hanging from it).

There are life preservers that on contact with water (for more than a seconds) will auto-inflate using a CO2 cartridge.  I'd look for something similar you can put on your cabin/cockpit to help it maintain buoyancy, having it on your wings won't do any good, it would leave your cockpit underwater still.

@ivanivan its better to have a manual inflation when dealing with open cockpit aircraft. It is possible for him to get wet in the cockpit from condensation and actual rain and have  the vest inflate by accident which could cause an accident unless it is a flight rated item.

Not practical to put balloons in the wings.  They would expand at altitude, messing up the wing profile.  How would you control that?
The best option, possible if the fabric is reasonably impermeable, is to seal all possible ingress points in the wing, leaving a small vent hole at a point least likely to be submersed, like the wing root trailing edge.  This will at least delay the sinking.   You could use ripstop repair tape used for fixing tents.
That'll slow down the sinking process, giving you lots of time to get out.  Then wear one of those compact inflatable vests that boaters use that drape around your neck that you inflate when needed, for swimming to shore.
Even better, with all the weight you would add with various other solutions, might as well get a set of Puddle Jumper amphibious floats.  Might as well make it possible to land on water anyway.  Problem solved.

I didn't think about the air expanding, lol. I never go higher than about 5000 or 6000ft, but I can imagine a balloon would get bigger!

Yes at 6000 ft the atmospheric pressure has dropped by almost a quarter from what it was a sea level.  Some commercial aircraft use tape over rib lightening holes at the tip rib and any holes along the spar that go into empty spaces in the wing structure to delay sinking of the airframe if ditched.

About the inflatable vest: never inflate it before you are clear from the aircraft... or you'll think whit it!

Literal balloons probably won't work well.
Balloons aren't safe, puncture-resistant flotation devices. Most will puncture if damaged. Also, their location is too far overhead for personal safety. Also, balloons leak, so you'd have to refill them every once in a while, which would be very tiring.
For personal safety, one option is getting a HEED, also known as Spare Air. They have a bad rep, but their initial purpose was getting out of a drowning helicopter, and that's where they do work. It does require a bit of training to use safely, but mitigates more risks than it adds.
Keeping the plane afloat would probably require something tougher than balloons. Sealed lift bags are flatter, easier to refill, and won't tear as easily. But the fuselage will still sink, and keeping it afloat gets into more unorthodox solutions with inflation, which add their own complications.
It's more important to make sure you have a PFD and signaling equipment yourself - even for a good swimmer, staying afloat for a long time is exhausting.

Weight, complexity, risk of unintended inflation.  Solution needs to be passive.

You have a point. But I don't see how a passive solution could do all the work. Weight-wise, it's a few pounds. Inflated buoyancy devices are a standard solution even on modern airliners (for personal survival).

I would be extremely vary of scuba gear in a case like this. It only takes about 3 m (10 ft) ascent with held breath—which may easily occur in the state of panic—to get pulmonary barotrauma and that is often fatal.

Also, keeping the plane afloat by the wings won't help a iota, because the gondola is likely heavier and therefore will rest below the wing, fully submerged.

That's fine.  It just has to not sink to the bottom right away, long enough to get out of it.

@JanHudec The Spare Air is a rebadged HEED, specifically designed for escaping ditched craft. Adds its own risks, but it was deemed to reduce more than it adds.

I think the Personal Flotation Device is definitely going to be a part of this. Thanks Therac.


text:
What is the difference between nautical air miles and nautical ground miles?
What is a simple way to understand the difference between the nautical air mile (NAM) and the nautical ground mile (NGM)?
How does the wind affect the net displacement of the aircraft as that is the only differentiating factor between NGM and NAM? (NAM by definition does not include the vertical displacement or the altitude gained by the aircraft.)

For further reference to mathematical formulae defining the above terms:
https://www.theairlinepilots.com/forum/viewtopic.php?t=320
From my deep dive in the quest to unravel the mystery of NAM and NGM, with inspiration from the BELOW answers I'm able to conclude with a couple of points:

NAM and NGM are same if wind is still

NAM measurement is independent of the wind and depends solely on the movement of the aircraft relative to the air around it. NGM is a dependent quantity which solely depends on the wind ie. With a Headwind component NGM is lower than NAM and vice versa for tailwind condition.

The usage of NAM was most prevalent in older flight planning systems for long range cruise before the age of FMCs which do the same thing electronically, NAM provides a database of performance of an aircraft in various phases of flight independent of the wind, to which the wind correction maybe applied to determine the practical value.

Is this a question about the distance covered through the airmass versus the distance made good over the ground?  I hate to see a question about elementary physical concepts turned into a question about the definitions of certain phrases, which are arbitary.  In a typical ground school course you won't be taught anything about a thing called an "air mile" or a thing called a "ground mile".  Ask a pilot about the meaning of a "NAM" or a "NGM" and many will likely give you a blank stare.  These sets of initials aren't necessarily widely used in aviation, though I'm sure they have their niches.

Re "(NAM by definition does not include the vertical displacement or the altitude gained by the aircraft.)"-- where did you get this definition?  And what does that same source say is the definition of a NGM and a NAM, and how are they different?  There's your answer.  If we are flying in a horizontal path over Mt Everest, would the NGM distance include the effect of the height gain and loss that we would experience if we were hiking on the ground rather than flying?  Hope to see that cleared up in a self-answer by the OP, as only he knows what source is he is relying on for these definitions.

I think the key is in learning to draw the vector triangle showing the effect of wind; see my anwer.

Regarding your edit, I'm not sure what kind of "deep dive" you may have performed to unravel this "mystery", but the effect of wind is pretty basic when you think about it, and is something every beginning student pilot is expected to know.

I didn't intend to be toxic, it's just that the effect of wind on ground speed and track can be instinctively understood and is well documented, here and elsewhere.  Your question didn't show much evidence of any prior research, and questions are often closed for this reason.

Now who is being toxic...

@Darshan Patil - To be clear, I am NOT triggered or offended in any way by mundane questions.  And again, my intent was not to belittle you.  I apologize that it came across that way.  You posted a link to an airline pilot discussion board, and I wanted to clarify for you that airline pilots already get this, and that student pilots are expected to know and understand it by the time they get to the cross country planning stage of training.  That's all.  While it may be instinctive to me, I don't automatically assume that a non-pilot would understand right away.

@MichaelHall I understand the affects of the wind on the GS quite well.The terminology is misleading and needed clarification. I was conflicted about its simplicity, as FMSs use this formulae as a part of its code and these formulae fall apart at 0 kts GS,which is a possible scenario.I am a fellow commercial pilot as well. Before you continue this thread, I would ask you to understand the mathematics behind the derivation of the formulae which give perplexing results .While the math may be instinctive to me, I don't automatically assume that a non-engineer would comprehend right away.

A nautical ground mile is one nautical mile over the ground.  A nautical air mile is one nautical mile through the air mass.  This distance can be different because of wind.
For example:
If you are flying at 100 knots true airspeed in a zero wind condition, nautical ground miles will equal nautical air miles.
However, if you are flying at 100 knots true airspeed into a 100 knot headwind, your nautical ground miles will alway be zero, regardless of how many nautical air miles you fly for (at 100 knots).
Anything in between will result in some variance affecting the “net displacement of the aircraft”.  This variance can be calculated using the basic wind triangle.

would it be different due to altitude? i understand that it's small effect (421 vs 420 miles on 3 mile altitude) but still

Historically a nautical mile was 1 minute of latitude along any line of longitude, but note that the distance corresponding to 1 minute of an arc depends on the radius.... The modern definition has 1 nautical mile be exactly 1852m. So if the nautical air mile inherits the older definition then altitude matters (slightly), if using the modern one then it does not.

I understand the effect of altitude, but the question specifically said to exclude that from consideration.

Why would "nautical air mile" be infinite? If your TAS is X NM/hour, then the airmass has moved X NM in one hour relative to the aircraft, regardless of winds. Stable winds are only a consideration when ground is concerned.

Staying in one place (ground) has nothing to do with air. What you wrote there is just incorrect if your definition of "nautical air mile" is "one nautical mile through the air mass".

@JZYL: The answer is saying that some journey (over some ground distance) will take infinite air miles, because the ground speed is zero.  Not infinite air speed, but rather infinite total time.  The usefulness of making the point this way is questionable, but it doesn't look like a technical error.  (Except that no specific ground distance was ever mentioned.)

@PeterCordes Mile by definition is a unit of distance, not time. It's completely technically incorrect. I understand what it's trying to say: that it will take an infinite amount of time to go from A to B. But the interpretation is not the issue here.

@MichaelHall See above for why it's incorrect.

@JZYL: On 2nd look the sentence is inconsistent with itself. The sentence structure implies doing this for some finite time (and explicitly says 0 ground miles).  We can rule out infinite time because 0 * infinity is undefined, not 0.  But then the 2nd half of the sentence assumes infinite time for a non-zero journey distance as 0 speed.  Nowhere was that concept introduced, so it's only technically correct for a different case than it's talking about.  You can't go through infinite air mass in finite time at finite airspeed.  I think it would be clearer to just talk about speeds, not dist.

Right, ground distance will always be zero in that case, that wasn't the problem.  Nothing about that implies infinite time.  You're unnecessarily introducing the complication of an infinity into your example.  I left a suggested edit that avoids that but still makes the same point.  It should fix the problem @JZYL and I are pointing out.

Nor does anything imply finite time, other than the issue of rate.  But, as you point out there is no need to complicate things by using infinity so I accepted your edit, and will clean up extraneous comments.  (Isn’t “fly for” a dangling participle or something?!)

How does the wind affect the net displacement of the aircraft...?

Before we worry about the definitions of certain phrases such as "nautical air mile" and "nautical ground mile", we should learn to draw the vector triangle of (true) airspeed, wind, and groundspeed, assuming that the flight path, the earth's surface, and the wind are all horizontal.  The ratio of miles covered through the airmass to miles covered over the ground is identical to the ratio of (true) airspeed to groundspeed.
In the vector triangle of airspeed, wind, and groundspeed-- overlooking for the moment the difference between "true" and "indicated" airspeed-- we can say that the airspeed vector represents the "inherent" performance of the plane, given the position of the throttle or thrust lever, and the position of the elevator control which determines the wing's angle-of-attack.  For a given thrust and angle-of-attack, the wind has no effect on the airspeed vector.  The plane is flying "inside" the moving airmass and not directly "feeling" the wind.  The plane's "inherent" performance won't be enhanced or diminished by the wind.  But when we add the wind vector as illustrated in the link above, then we can find the groundspeed vector which shows the actual achieved performance over the ground.
As for your implied question about the difference between a "NGM" and a "NAM", the most logical meaning of the "NGM" distance would be the distance coverered over the ground, assuming flat ground, expressed in nautical miles, while the most logical meaning of the "NAM" distance would be the miles covered through the airmass, assuming a horizontal flight path and a horizontal, uniform motion of the airmass, expressed in nautical miles.  However, we should be clear that there is no actual difference between the length of a "Nautical Ground Mile" and a "Nautical Air Mile".  To make it clear that we are talking about two different quantities of interest rather than two different units of measure, it would be better if we spoke of "distance covered through the airmass" and "distance covered over the ground", rather than "nautical air miles" and "nautical ground miles".

Thank you for the reply! I'm familiar with the concept of wind triangle, and the explanation makes perfect sense. The only part that I'm still not completely convinced is the NGM and NAM explanation as these are distinct terms used in flight planning and hold different mathematical formulae per my observation.

If you understand the wind triangle then why are you asking this question?  The difference is the distance covered over the ground vs through the airmass.  That’s it.  And I disagree that these terms are used in flight planning.  Not commonly anyway.  Not by people I have been flying with.  Ground miles are simply called miles, and air miles are only important as they relate to ground speed and time.  Nobody cares how many miles you flew through the airmass.  It isn’t measurable like time and distance are.

@MichaelHall -- have you ever seen a photo of an "air distance computer"?  I would provide a link but I can't find one right now; more later.

Do you mean air data computer?

These are very strange terminologies. As far as aeronautics is concerned, we care about these things:

Airspeed: speed of the aircraft relative to the local air-stream; this is important for keeping the airplane afloat
Ground speed: speed of the aircraft relative to the ground; this is important for seeing how fast you may be getting from point A to B
Maybe, ground distance: total distance moved along a [curved] trajectory

Ground distance, which could be expressed in Nautical mile, would be an integral of the ground speed. Maybe you can call that unit Nautical ground mile.
The integral of airspeed, however, is more or less meaningless. At best, it states how much distance a parcel of air has traveled relative to the aircraft. But since winds change over the trajectory, it wouldn't even be the same parcel of air. The unit of that distance could be what you called Nautical air mile.

Meaningless seems overstated as is not fuel usage based closer on  integral of airspeed than integral of ground speed?

@chux Not really. Neither is a good gauge of fuel usage. If you're climbing at 5000ft/min at any particular airspeed, the fuel usage would be drastically different than descending at idle throttle at the same airspeed.

Although, I have never heard the term Nautical Air Mile, it does make sense. Based on your attached link, an NAM would be the distance from a particular parcel of air. Airspeed would be the speed at which the aircraft is moving through, towards or away from particular parcels of air relative to those parcels. Airspeed is also the speed at which parcels of air are moving towards or away from a particular relative point or object.
Ground distance can be measured directly. So can time. Therefore, groundspeed can be calculated. Groundspeed and airspeed can also be measured through its affect on our instruments relative to the instruments themselves. Measuring NAMs directly seems impractical if not improbable. The most direct way that comes to mind is the movement of radiosonde balloons. Otherwise, NAM can only be calculated from other metrics. I find it difficult to think of any useful application of nautical air miles in practical use.
Also of note, in aviation, nautical miles is generally in reference to the distance between two point over which we are flying. Slant range in nautical miles takes into account the straight line distance between the aircraft and a point on the ground taking into consideration the aircraft’s altitude (the hypotenuse of the right triangle). When an airplane’s ground track is affected by wind, its measurement of airspeed vs wind speed is still relative to the ground. But, sense a nautical miles is defined as 1 minute of arc distance of latitude, it makes sense that it would be slightly greater in the air than on the surface of the Earth.

So this answer is saying that the higher the altitude, the larger the number of feet or meters contained in a Nautical Air Mile?  I  understand the rationale for such a suggestion, but I doubt that this answer is harmonized to the definition of a NAM in whatever source the OP is relying on for definitions of these concepts.

This is a good answer, but the OP specifically excluded any altitude effects.  Also, if you click on the link that spawned his question they are discussing the wind triangle.

@MichaelHall - Thanks. The link was added after my answer. That helps to bring context to the question. Although, I still question the usefulness or relevance of knowing your distance in reference to a particular parcel of air. It seems more academic than practical. However, using the wind triangle to determine other metrics like groundspeed, ground distance, relative motion across the ground, heading vs track, and time of flight are very useful, relative, and important.


text:
How do I determine holding pattern entry and direction in this example?
I need help with this question for the IFR written test: "A pilot receives this ATC clearance: '...CLEARED TO THE XYZ VORTAC. HOLD NORTH ON THE THREE SIX ZERO RADIAL, LEFT TURNS...' What is the recommended procedure to enter the holding pattern?"
Why is the answer on the left the correct visualization? It doesn't say if I should hold left or right of the radial. Both answers are left turns. Both answers are holding north. What am I missing?

Thank you all for your help. My 150 arrow was wrong and I was confusing myself. Also, it's helpful to know that the inbound leg terminates at the fix (which entirely makes sense now). So, my new answer is direct entry and here is my new visualization:

Neither of the two representations show holding North if the arrow depicted in the corner is truly pointing towards 150°. If this is the case, North is at the bottom of the page and South is at the top. Therefore, both representations are showing holding South of the fix.
If the dot depicted is the fix, the representation on the left is not a holding pattern. Holding patterns have their inbound leg terminating at the fix. Your turn towards the outbound leg would then begin when crossing the fix on the outbound leg.
Furthermore, your HSI is showing that you are on the 150°  To-Radial of the fix, on a 155° Heading, and a 16.5 DME. This would put your aircraft inbound, 16.5 Nautical Miles North of the fix, roughly on the 330° From-Radial (or just Radial). You should intercept the inbound leg 360° Radial of the fix well before crossing it. Then effect a Direct Entry, Performing your 5Ts Once you hit the fix with wings level.
You could, however, continue direct to the fix, inbound on the 330° Radial, and still perform a Direct Entry. I just, personally, think it’s easier to intercept the inbound (360° Radial) leg first.
Research AIM 5-3-8 for further details.

Thank you! This is very helpful. I just edited my question to post my new visualization.

You're already on an intercept track flying the 330 radial, so a left turn to pick up the inbound track of the hold might look odd to the controller.  That being said, those entry methods are just protocols for efficiency's sake; you can enter a hold any way you want as long as you stay in the protected airspace and get established on the racetrack in a reasonable time.  Once you start using an FMS, the software works it out for you and you never have to figure out which one to use again.

@John_K . . . with the caveat that you do have to interpret the holding instructions and program it into the FMS correctly, which presumably have been given as there's no database/published hold matching the instructions.

The holding clearance that you have specified is invalid.
CLEARED TO THE XYZ VORTAC. HOLD NORTH ON THE THREE SIX ZERO RADIAL, LEFT TURNS...
You cannot hold north of the VOR on a radial that is south of it.  A correct clearance would be
CLEARED TO THE XYZ VORTAC. HOLD **SOUTH** ON THE THREE SIX ZERO RADIAL, LEFT TURNS...
Conversely, the hold that is drawn on the left is incorrect because you are turning into the holding point.  You always fly a straight segment into the holding point.  The arrows are backwards.
If I was given this corrected hold and flying a heading of 150°.  I would end up flying a parallel entry.

The corrected hold could also be:
`CLEARED TO THE XYZ VORTAC. HOLD NORTH ON THE ONE EIGHT ZERO RADIAL, LEFT TURNS...
In this case, I would end up flying a direct entry into the hold.

“You cannot hold north of the VOR on a radial that is south of it.” Could you clarify this statement, please. It is a little confusing. The 360° Radial of a VOR is a line with its origin at the VOR and its direction stretching Northward. Although, in application, the 360° Radial is a line stretching both North and South, with the VOR at its center. The To-From indication would determine whether the aircraft were sitting on the 360° Radial to the North (From indication) or the 180° Radial to the South (To indication). Heading and Bearing would determine whether you are facing the VOR.

If you were to look at it this way. A 360° From-Radial at 16.5 DME (5000’ MSL) is the exact same point (Lat-long) in space as a 180° To-Radial at 16.5 DME (5000’ MSL). You would be at a point on the 360° actual Radial. At that point in space, a Heading of 180° would roughly place you going towards the VOR. A Heading of 360° would roughly place you going away from the VOR. The Bearing of the VOR would be determined by whether you wanted Magnetic, Relative, etc.

Yeah I had a problem with that one too.  The radial itself is the track extending from the station at that compass position.  The clearance would be hold on the 360 radial, inbound track 180, left turns.  I think his arrow on the sketch means he's heading towards the VOR on the 150 radial, not a 150 deg heading.  I think the right sketch is correct for a hold on the 360 with left turns, and what was missing is the inbound track reference, which would eliminate the confusion (maybe done on purpose).  In my opinion, the correct pattern is the right one, and the correct entry would be parallel.

@JohnK - Maybe. Although, if the HSI represented is part of the question, the aircraft is on the 330° Radial with a Heading of 155 and a DME distance of 16.5. This would put him inbound to the VOR from the North by Northwest.

Oops you're right I didn't even look at the HSI.  Yeah you're right both those sketches are wrong.  The hold should be the right diagram flipped over so the track pattern is on the lower left instead of upper right, and the entry would be direct.

"Hold North" means the holding pattern must physically lie North of the VOR/holding fix. It does not indicate the direction of the inbound course. "Radial 360" then narrows it down. The only way to Hold North on Radial 360 is for the Hold to to be defined by an inbound course of 180 to the VOR. This kind of instruction is more useful when the holding fix is not the VOR but defined by Radial and Distance from a VOR. e.g. if the holding fix were Radial 015/20DME Hold North would mean an 'inbound course' of 195 whereas Hold South would mean an inbound course of 015 to the fix.


text:
You are flying an IFR trip in a Cessna 172 and you receive a pilot report (PIREP). It is useful if:
Practicing for my IFR written test. Question is in the title. Three options:

A) It is current and reported by a similar airplane to your own.
B) The report is given by a professional pilot—for example a Boeing 747.
C) The pilot is reporting icing conditions and is flying a jet
airplane.

I would have thought the correct answer is C because if a jet is reporting icing, the 172 will also have trouble. But apparently the correct answer is A, which I guess is also correct but in my view less useful if it's not reporting anything. What am I missing?

I know less than you but it could be because the jet pilot is flying higher or flying in IFR while you are in VFR

Don't worry about it, some of the FAA written test questions don't make much sense.

You can rule out B because Boeing 747s are not actually "pilots".  ;)

Flying a single-engine Cessna, you are unlikely to benefit from a PIREP provided by a plane flying 25 000 ft above your cruising conditions.
There is usually some trickery involved in FAA/EASA tests. It may be that a 747 provides a PIREP while climbing, thus being helpful to you, but in most cases PIREPs from jets are not that helpful for single-engine piston aircraft.
As general advice, make sure you read the questions carefully, and understand what it is they are asking. Some of the questions are such that all of the options appear correct, and others may be such that none of the options seem correct. You have to pick the one that is most right or  not wrong in any aspect. It's all about context.

(A) makes sense because the other two options are a bit open ended. (A) has all the information you need to judge whether it's a potential correct answer or not. If the 747 is above the FZ LVL, you don't need to worry about that (unless you take your skyhawk above FZ LVL and in visible moisture- then you should!). No matter what the PIREP always has to be current. Also, how professional the pilot is in general and proficient in giving PIREPs don't necessarily depend on what A/C they fly.
Agreeing with Jpe61, as a pilot you're primarily looking for information that pertains to your flight. Read the PIREP (or any other Wx report for that matter) and see what information pertains to your type, altitude, route, etc., of flight.
However, that does not always mean that just because the information doesn't directly point toward your area of concern you should ignore it. You can always take every small bit of information to construct a broader, general "big picture" of what's going on in the skies and that's what your job is as a pilot. Something happening way above you might give you some ideas to what could follow in the next couple of hours at your flight level.
..
From an exam POV: in Canada, TC has a lot of questions where more than 1 option makes sense but they want us to select the option that makes the most sense for our scenario or in certain cases will give us the least bad outcome/most chances of survival.
Most (if not all) aviation exams focus on practical thinking. So, if the answer's not that straightforward, think about what you would do in a real world scenario like that.

I would say that the correct answer is A)
First off, you need a pilot report to be current because it is as an onsite weather report of what’s going on in a specific location in space at a specific time. It’s not much help to you if the report was made two days ago. Second, a pilot report made by a pilot in an aircraft similar to yours is far more useful to you, because it’s going to be a similar configuration, wing loading and planform, similar airfoils, similar performance characteristics, similar onboard systems, and similar operating altitudes and airspeeds to your own aircraft.  This is important for dangerous kinds of weather such as thunderstorms, icing, windshear, turbulence, etc.  While a PIREP made by a professional pilot in a large jet is nice, it may not be relatable to your situation for the reasons given above, and, so long as it follows the correct format, will provide you with the same information any other pilot can provide, professional or not.  Therefore we would rule out B). The same applies to answer C).  While a PIREP that contains information about icing conditions can be useful to you, it may not be relevant to you in a Cessna 150 cruising at 4500 feet and well below the freezing level when it pertains to icing conditions encountered at 16,000 feet at 380 KTAS.  Therefore, we eliminate answer C), leaving A) as the correct answer.


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How and why does the ATR-72 sometimes use reverse thrust to push back from its parking position?
Travelling with Czech Airlines via Prague in an ATR-72 I have already experienced multiple times that instead of pushback service the planes simply used their reverse thrust to leave their parking position, even doing a 90° degree turn while rolling backwards.
Personal experience as well as a Google search show that this is rather uncommon. What makes the ATR-72 special to be able to perform such kind of manoeuvre?

Related

Was it really powering back from a gate (with a jetbridge and co.)? I've never seen an ATR-72 parked at a gate in PRG, I think they exclusively park on the apron (and board via buses), which means they have lots of room around them for powering back and also that no pushback tractors are typically around.

@TooTea Yes, as you correctly assume this was on the apron and not at a gate. However, I still find it quite unusual.

@TooTea Ah, now I see why you are asking - someone edited the title of my question. Fixed that.

As other answers note, for most aircraft, the risk of the engines ingesting FOD while powering back is too high. This is particularly true for turbofan engines mounted under the wings.
Turboprop engines tend to be mounted on high wings (such as on the ATR-72), and they tend to serve smaller airports where an airline may not have tugs available for pushback. Regional and private jets, which often have fuselage-mounted engines, also tend to serve such smaller airports. These planes were designed with the engines mounted higher specifically to reduce the risk of ingesting FOD, thus allowing them to safely power back when needed.
Note that powering back still burns a lot of fuel, and even with high engines the FOD risk isn't zero, so when operating at larger airports that do have tugs available, airlines will generally use them.

Pushback via reverse thrust is problematic for turbofans, as they kick up lots of debris, which could be ingested into the engine or hit something laying around.
Presumably the ATR as a turboprop doesn't create as much wind, and with a turboprop the reverse thrust is blowing from the front of the engine, so there's no chance the debris will reach the intake.

Most modern commercial airliners are prohibited to power back. Ground operations in aircraft fitted with high-bypass engines are usually restricted to idle and low-idle operations (enough to make the craft start moving, after which momentum enables further movement with idle only). Aircraft capable of power back are predominantly thus turboprops, several operators of these allow their crews to operate accordingly.

Is a powerback allowed by airlines as a safe maneuver?
Related: Is it possible to use thrust reversers to taxi backwards?

Turboprops have two key advantages over turbofans when in reverse: not only is the intake smaller and higher off the ground, but the thrust point is forward of the intake and thus less likely to lift FOD towards it.

I wouldn't say that there is NO chance of FOD..  Engine intake is below the engine on the ATR-72, the prop is pulling air forwards as shown on your diagram, engine is pulling in air at the same location.  Any FOD that the reverse thrust picks up could just as easily enter the engine.

One big popular exception was the MD-80 which used to routinely powerback with its elevated tail mounted turbofans being high enough from the ground to reduce the risk of FOD ingestion.

Just about any turboprop or piston engine airplane with reversing propellers can do it, as the airplane doesn't care whether BETA reverse is being used on the ramp or a taxiway or a runway.  You normally use DISCING (flat prop blades to make zero thrust) when taxiing when you want slow down or when you are stopped.  To go backwards, you just move the powers back out of DISCING a touch.
You kick up FOD on the ramp, which a TP can draw in almost as easily as a jet. Gate areas are a garden of zipper tags from luggage and will do major damage to a TP if they get past the particle separator in the nacelle, which is more likely on the ground without a high velocity air stream to let the separator do its job.  The airline has probably made the business decision to take the risk of FOD damage to avoid having to use tugs for pushback.
When you want to stop backing up, you should not use brakes, lest you tip back.  You use forward power.

You can do powerbacks with basically any commercial turboprop, not really uncommon at all. We did it regularly with our F50s and we still performing  it nowadays sometimes (even though quite rarely) with our DH8Ds when there is no towbar available.
Never heard about the problem of ingesting FOD, we never experienced this. The only thing you have to be careful about is NOT to use the normal brakes for stopping or you will end up with a tailstrike. Instead one has to go back to DISC.


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Why do military jets sometimes have elevators in a depressed position when parked?
Why do they have elevators in such a position as if the joystick is pushed forward, even though there's nobody inside the cockpit?

Gravity? ........

They're depressed because they would rather be flying.

Is there any trend or habit for pilots to push the stick forward to make exiting the aircraft easier?

FWIW, while I won't dispute the accepted answer for this particular case, you will find that for a lot of smaller airplanes -- e.g. 4- to 6-seater piston-engine general aviation airplanes -- you'll see the elevator in this sort of fixed position as a result of a "control lock" installed inside the cockpit on the controls themselves, which intentionally puts the control surface in this position to guard against gusts of winds (both to keep the control surface from flapping in the wind, as well as to ensure that lifting forces generated by the wind push in the least-disruptive direction)

It generally means that the hydraulic actuator (power control unit) driving the surface has an "idle" facility that allows fluid to move internally between the two sides of the actuator piston, or just circulate in the pressure/return lines, and when unpressurized it acts more or less like a hydraulic damper even though the input spool valve is at its "null" (no command) position.
The result is that when unpressurized it's free to move (although damped) and if gravity wants to pull the surface in one direction it'll do so.  As soon as hydraulic pressure is applied, it'll snap back to whatever position is being called for by the input system.
Sometimes you have PCUs that are "non-idling" and when unpressurized they are hydraulically locked which is only broken when there is a control input to the controlling spool valve.  Such surfaces stay where they are even when the hydraulic pressure has bled off, unless you move the controls to break the hydraulic lock.
On the CRJs, the elevator PCUs are idling, and the elevators sag when unpressurized.  The aileron PCUs however are non-idling, and the ailerons don't sag when unpressurized. If you try to move an RJ's aileron when its hydraulics are off, it is totally rigid.

It's probably also worth mentioning that putting the centre of gravity of the elevator (taileron?) behind the pivot is also a deliberate choice. It helps to reduce flutter and smooths the response to turbulence.

Not quite like that. For unpowered surface you DON'T want the surface's CG aft of the hinge line because this encourages flutter,being a complimentary oscillation between the control surface and the wing it's attached to, and usually requires balancing the surface to put the CG at or forward of the hinge line. However, when the surface is hydraulically driven, you can take credit for the rigidity, and when unpressurized, the damping ability, of the hydraulic actuator(s) to prevent the mutually reinforcing oscillation of flutter from getting started, so they get away without balancing.

Canadair Regional Jets? None of those look like passenger planes. https://www.google.com/search?q=aircraft+CRJ

Hydraulics are hydraulics.

Doesn't this imply that loss of hydraulic pressure during flight could result in a crash?

If the airplane has a single actuator driving a critical surface, and that actuator becomes depressurized, yes of course.  Civilian transport airplanes have to have redundant actuators to eliminate single-points-of-failure like this.  Military airplanes may or may not.

@JohnK are you saying that "CRJ" in the last paragraph of your answer really does stand for Canadair? If so I still don't understand. Why call out one particular manufacturer?

Just an example of an idling vs non idling actuator driven control surface.  I used those as examples because I know the systems and most people have observed these airplanes on the ramp if they've ever traveled by air.  Military aircraft operate with similar components but different and often less stringent redundancy requirements.

@John K's answer is perfect. However, in other mechanical systems such as elevators, fork-lifts, factory machines, etc and also NON hydraulic systems (and also possibly Jets) it is designed to be so so that when the machine is idle/switched-off the system is in a 'non-stressed' state or in a 'safe state'.
The keywords are 'design' and 'requirement'.

As @Makyen 'requests clarification' -  lifts (elevators) have a safety feature for power-loss/(electronics) failure conditions. The battery backup brings the lift to a safe 'landing position'and stops and opens the doors {if the lift was moving during a power loss} (the CPU, in modern lifts decides on the best location). Lifts also have a mechanical power independent system that locks the lift mechanically on a safe position which can be the closest floor. Lifts have many safety features. But my  point is, to the original question, there is a design requirement which is well planned and thought of rather than a 'random' choice. Similarly for jets the requirement, as someone else pointed out is (possibly) to keep the jets on the ground during heavy  winds/storms, but the design also takes into consideration idle stress, energy consumption, etc- a win-win situation.I would reliably assume that fighter jets have much, much more redundant/safety systems to maintain reliability and serviceability.
As for fork-lifts, I am not talking about hold-shutdown positions. There is a training requirement and also storage zone requirement for forklifts. It would be unwise to store a forklift/crane in a loaded/stressed position due to safety requirements, etc (just like when the jets are 'stored').
Ref: Outage safety also 'informative'
FYI: I am ISO-9001 (1993/1994) certified/trained in service engineering. Also, at that time I was acquinted with one of the Airbus-A340 designers - my favourite plane (the 747 gets an honourable mention).  My favourite jet is the MIG-21 (the F-16 gets an honourable mention) (although there are newer ones that are better). My  uncle flew for the RAF during WW2 and another was a mechanic for the F-4, etc (received a lot of knowledge from them)...

Trust this helps.

It does help indeed, welcome to the community! :)

Do you really think elevators are designed to gradually move to some equilibrium location when the power is lost? That would be completely unsafe. They are designed to stay at the same location as they were when the power was lost. Forklifts, also, are designed to hold the current position of the hydraulically operated parts when power is lost/turned off. To do otherwise would be a safety concern. The only forklifts I've seen that didn't hold position were know to have hydraulic leaks. If you meant something other than the opposite of what I've described, then please [edit] to clarify.

They put fork lifts like that to avoid wear on return stop valves and other hydraulic line components. Resting against the ground is the only way to ensure that the system is de-pressurized and not resting on a normally-closed return valve etc. Splitters for instance, do not like backpressure differences. (a splitter splits oil volume equally to two lines when operating - if you want to lift two points with equal rate but unequal weight, for instance.)

This is a safety feature.  You don't want the airplane to blow over in a strong wind.  With the elevators down (as you see them in the pictures), a gust from the front will push the plane's nose down and keep the main wing from generating lift.  A gust from behind will push the nose up, but in this case, the main wing will present its top surface to the gust, and will push the airplane back down.  Either way, you're safe.
@zymhan: My main source is my flight training.  I was taught not only to park the aircraft with the controls locked in a position that kept the aircraft from blowing away, but also to move the control surfaces while taxiing to keep wind from getting under the wings.  Taxiing into the wind, we keep the elevator down (pushing the nose down); turning a corner so the wind was from abeam, we deflect the upwind aileron up (pushing that wing down); etc.
Small general aviation planes like I fly can easily be picked right up and flipped over by a strong gust.  Even if you've got them tied down, you never want to risk one of your knots coming out or an old rusty clip breaking, leaving your airplane free to go tumbling across the airfield.  Leaving controls in the right place takes some of the stress off the tie-downs.  Every little bit helps.
Modern fighters and larger aircraft won't just up and blow away unless you get into a serious storm, although serious storms do happen, especially on aircraft carriers at sea.  The greater risk to large aircraft is more prosaic: you don't want them to tip backward and knock their tails against the tarmac.  At this point, we're beyond the scope of my pilot training and into the realm of my aeronautical engineering degrees.  Aircraft landing gear is designed to place nearly all the weight on the main gear.  The mains are located just slightly aft of the c.g. so that on a hard landing, they take most of the shock, and the nose doesn't snap down violently onto the nose gear.  This lets you design the nose gear to be as light as possible, and the structure that supports the main gear as short and light as possible.  However, with not much weight resting on the nose gear, the drawback is that it doesn't take much wind to lift the nose up and bang the tail against the ground.  Many planes have tailstands to prevent this.  But again, parking the plane with elevators down is just that much extra insurance.

This is a very interesting point, but do you have any sources for it?

Fighter jets may be stored on the edge of aircraft carriers, in bad weather. That means it is very important - so I think the feature exists and is intentional.

@Volker: While that's good logical thinking, I doubt it applies to jets on aircraft carriers. Six to eighteen chains tie down the aircraft, depending on weather and ship maneuvers.

Saying that wind would 'push the nose down' is a bit misleading anyway - what it will do is lift the tail upwards, which doesn't sound like a desirable outcome to me.

Actually high winds can snap chains. Happened to a buddy of mine. Heck of a way to loose an aircraft. He now prefers steel tie downs to aluminum.

This answer is what I was guessing (I.e. it makes sense to me that I’d want to store airplanes this way in case of wind) but would be much better with a source.

I understood it to be about lift. With surfaces down stray winds from the side won't create forces that could tip the plane over.

@Nav Yes, but they need to be taxied to an from the location, in a hurry. It's possible to control them while moving on deck, of course.

Same principle in small aircraft as all aircraft control column locks hold them in place
All explained above by other posts it is not a fashion or pilot habit it is part of post flight check list ensure control lock is in place

It's not a control column lock, as explained in the other answers.


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What are the most challenging taxi manoeuvres that a typical commercial airline pilot must execute?
I am currently involved in a University level modelling excercise which looks to investigate the handling qualities of a novel nose wheel steering system.
As part of this study, I am interested in understanding what are the most challenging taxi manoeuvres that a commercial airline pilot would typically execute, both regularly, or in special circumstances.
Some specifics for the question:

I am primarily interested in answers from pilots of Single Aisle
sized airliners (A320 family, 737 series, etc.), although general
cases are also welcome.
I am interested in the kinds of manoeuvres which place the highest demand on the NWS system in terms of responsiveness, max rate demand, etc.

@Mark's comment on one of the answers suggests researching causes of taxiing accidents or overruns may be a good place to look for more ideas on what can be done to improve nose wheel steering systems.

"Most challenging" is a matter of opinion, but if I were to pick, it is probably the 180 degree turn.
The purpose of the maneuver is to turn the aircraft around and face the opposite direction. The technique is to position the aircraft to one side of the runway (taxiways are generally too narrow for this), then apply maximum steering angle, minimum thrust as well as differential braking (i.e. braking on the inner set of wheels only).
The challenge is that the nose wheel, outer set of wheels, outer wingtip and the tail each have their own turning radius. It is made even trickier when the nose wheel is a good 20~30 feet behind the cockpit. The pilots will be above the runway grass while the nose wheel is still on the pavement.
This maneuver is challenging enough that most aircraft manuals I've seen (e.g. B737, B777, A320) dedicate a good 10~20 pages just for this. Here is an example diagram for the B737-600:

B737 FCOM Volume 2, Section 1.10.7
This maneuver is mostly executed on small airports where there is no taxiway connecting to the end of the runway. For example, the only taxiway connection to the runway might be at the runway's middle length. A plane that wishes to use the full runway length to takeoff will have to turn onto the runway, taxi down half its length to the end, then execute a 180. On large airports this is rarely an issue, although a 180 might be useful when part of the taxiway / runway is blocked due to an incident.

From an engineering perspective, the highest risk is probably any type of turn where side loads, or shear loads, end up applied to the nose gear (forcing a turn too tight).  Whatever new design OP has in mind would probably need to account for whatever worst-case tolerance is required in the case of pilots running too much thrust accidentally in a turn.

This matches up with my impression based on reports on AvHerald: most low-speed off-runway incidents occur when a large airplane turns around at the end of a runway.

Kevin, with an A380, does this "ever happen" ?  I guess it is literally possible but would it just be something that is never done?

@Fattie I vaguely remember an incident where an A380 en route to Sydney has to land at an alternative airport somewhere on an island in the Pacific where the runway was wide and long enough to land... but then the aircraft got stuck trying to do a 180 degree turn at the end of the runway.

A good example of a busy airport where this happens a lot is London City. They have to do it at the end of the runway (before take-off or after landing), and also do a similar manoeuvre when parking at the gate (though I don’t remember if it’s a full 180?), as they obviously arrive nose-in, but turn around to park nose out.

@Fattie here’s the story about that A380 diverted to Noumea: https://www.flyertalk.com/forum/14466516-post23.html When they landed they couldn’t do the 180 by themselves and had to be towed, but on take-off they could do it. Not sure if that was due to the crew change or if they just had time to prepare it.

My experience is on the CRJs up to the CRJ900.  I'd say the biggest challenge is going on the tiller at the end of the landing roll, and maneuvering on the ramp doing tight turns.  You are using a "steering wheel" with a really fast ratio compared to a car, no tactile feedback (just a light centering spring generally), and a small tire footprint below you, or on a bigger airplane, behind you, that has to change direction of a lot of mass.
Mainly, it's avoiding turning the nose wheel faster than it can deal with the moving mass. You have to learn to manage the rate of steering angle input vs rolling speed to minimize the side loads, which can really wear out nose wheel tires, or worse, causing side scrubbing of the tire (which you know is happening because of the vibration coming up through the floor).
Worst case I would say would be exiting a runway to a taxiway with a 90 degree turnoff and you've been braking hard to make that taxiway and maybe you are still a tiny bit fast when you get there and try to crank the tiller anyway.  Or trying to make a rally sharp pivot turn and starting to turn while rolling too fast, or turning the tiller too fast.  You can use brake to help the nose wheel with the turn, but that is kind of a intuition thing as well.
A great NW steering system feature could be something like a side load sensor that would adjust the gain of the steering control and back off on the sensitivity if sideloads got too high.  Kind of an anti-skid system for steering.

I'd have some trepidation about a system that decided I had turned too sharply, too fast, and limited the nose wheel movement.  Might be the difference between scraping the nose tires and getting the nose gear stuck in the grass.

I agree with you @nexus_2006, however, such a system may be the difference between getting stuck in the grass and snapping the nose gear due to to high a side loading. I'd rather be stuck in the grass in that situation...

I have to admit I would too.  It would be a way to cope with ham-fisted pilots, like the ones who get on the brakes really hard then let them off suddenly on the rollout.  Like how ABS on cars is to cope with people who don't know how to use brakes.

ABS, that's exactly what that last paragraph reminded me of. I imagine doing something like that on NW steering of a large plane is a heck of a lot more difficult to design correctly than ABS on a car though...

Re ABS, I don't want to suggest that anti-skid on airplanes is for the ham fisted.  Without anti skid just about everybody would blow tires all the time because it's extremely difficult to manually modulate brake pressure to avoid locking wheels when using hard braking with no A/S.  But I would take care to bring on maximum braking as gently as I could and try to plan ahead and ease the brakes off gradually at the end of the rollout, if pax was aboard, so they don't get jerked around.


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Why is there still an Air Berlin branded plane operating as of Sep 5th, 2018?
Yesterday, I flew from TXL and was quite surprised to see this during taxi:

It very much looks like people boarding an Air Berlin flight, an airline that supposedly does not exist any more. Local time was 12:20pm.
What happened here? Did some subsidiary survive the bankruptcy? Did someone buy the brand rights? Did they just not find the time to rebrand all the sold planes (in almost a year)?
Edit:
Since requested in comments: I do have another shot further to the right. Zooming in seems to reveal that the registration number is D-ABKM (or D-ABKW?)

Do you have another shot panned just a little bit to the right so we can see the plane's registration number?

It's just not repainted yet but thanks for this photo. I still have (useless now) Platinum One World membership card from Air Berlin.

Paintshops have been very busy in the past year.
So getting a slot to repaint an airplane is not that easy.
In addition, apart from the fact that the livery is not the one of the owner, the plane is perfectly fine.
And while applying a new paint scheme the airplane is not earning money.
What airlines do is, repainting the planes when a longer technical check is due anyways.

Is there anything in the past year which has made paint shops more busy than usual?

Repainting should happen during the regular big checks, but maybe extraordinarily extended checks and repaints for the former Air Berlin jets require more time (EasyJet, Lauda and Lufthansa). Lufthansa is also currently applying a new design to all jets, which will require several years. Even this design was redesigned, they made the deep blue a bit brighter. That shouldn’t cause extra work as said, because new paint is normal. https://magazin.lufthansa.com/de/de/aviation/im-neuen-kleid/

According to this page on Flightaware, the aircraft "D-ABKM" has been operating in and out of Berlin Tegel Airport (TXL) under the airline "Eurowings". We can therefore deduce that either Air Berlin sold the aircraft to Eurowings, or, sold it to an aircraft leasing company or simply terminated the lease and Eurowings leased the aircraft.
As for why it is still in Air Berlin livery, the other answer said it all - the operating airline considered it cheaper to fly it as it is than repainting it.

Eurowings added a bunch of former airberlin routes as part of a "rapid expansion" to take advantage of airberlin's failure. It didn't go so great, with many delayed and cancelled flights. I suspect taking aircraft out of service unnecessarily for a paint job is something they're trying to avoid until their operation is fully stabilized.